fuel level

[Vink27A]

I have spitting back every second stroke so I'm checking several possible causes. The level in he monoblock seems to be about 5-6mm to high, so that has to come down, does anyone have some suggestions?
I have two types off floats a plastic one and a brass one both show some wear where the needle seats on the float.

[1608]

I have had plastic floats that tend to stick. I prefer brass and the minute wear that bares on the needle shouldn't make much, if any, difference. Also, nsure that the spacer is in place on the float spindle.

[dave16mct]

This can happen if a washer/gasket is put under the needle housing (as in the new monoblocs). Some needles are different lengths too. Are you using a Viton tipped needle?
Dave.

[Les Howard]

If the fuel level in the float bowl is "5-6"mm too high, it will cause the mixture to be too rich not too weak, the most likely cause of spitting back....or tight inlet valve tappet...even a leaking inlet valve itself. However, I suggest it would be best to check the pilot jet first: Remove the small nut that covers the pilot jet and the jet itself can be removed with a vertical screwdriver. It could be tight due to corrosion, so get a good fitting one or grind one to fit perfectly. Check the jet size against spec and clean the jet hole with a small thin piece of wire. Don't worry, you won't enlarge the hole size. Even if you did, the variable mixture screw is there for perfectly setting the low speed/idling range mixture. As regards the fuel level being too high; it is unlikely, if you have the modern nylon float and correct needle valve. If you have the old brass one it can be distorted where the soldered-on lever pushes the needle valve bottom....Correct by truing up the angle by careful bending

[Vink27A]

I have 2 different floats (plastic and brass) but also 2 different floatneedles, they diifer a bit in length a assume that the longest one has to come with the plastic float?
There is also a difference in volume and weight between the floats so they won't rise the same.

[Les Howard]

Whatever the needle you use the longer needle will result in a lower fuel level in the float bowl. As said though. A high level of fuel will not cause spitting back... Remember it's normal for people to flood the carb before starting and the fuel level then is much higher....I'm just wondering if you are chasing the wrong cause? PS: The nylon/plastic float sometimes catches on the screw boss inside the float chamber slightly*...The screw is the one at the 7 o'clock position....Either file off the metal from the boss or even smooth off the nylon float at the touching point....You can view the action with an empty float bowl and move the float with a small screwdriver....see if it catches....
*...You can see that the float itself is further away from its pivot hole compared to the brass one...thus making the float nearer to the left side of the chamber.

[Vink27A]

Hello Les, I ordered a new float needle with a viton tip and wil also change the seat, we use cams with an "H" I assume that they have the same setting for the inlet valve (#3)? It can also increase the valve clearance for both, cold setting approx 0.1mm clearance for the inlet.

[Les Howard]

Hello Vink...The Viton tipped needle works very well...as long as the float can move freely. As long as the push rods can turn freely in the rocker arm cups the inlet valve should be closing no need for extra clearance. I mentioned the pilot jet might be blocked slightly...did you check this?...Spitting back is usually an indication of a WEAK mixture so check for air leaks at the carb manifold (O ring) and the gasket at the joint of the cylinder head inlet tract. Sometimes "spitting back" can be a sign of an ignition fault, like a bad spark-plug or even the points dirty or not set correctly or the condenser (capacitor). As a final suggestion: if the inlet valve lubrication is insufficient the valve might be failing to close reliably...check the oil screw setting in the rocker box...should be open about 1 1/2 turns (I think?)

[Vink27A]

OK thanks Les, I'll check these points, the pilot is new so it should be ok but will check it anyway, could the auto advance give problems?

[Pharisee]

...check the oil screw setting in the rocker box...should be open about 1 1/2 turns (I think?)

The general consensus is that it should be fully closed, then opened about 1/6th of a turn.